ANALYSIS OF THE FLOW IN THE GROOVES OF A MOLECULAR PUMP

Abstract

A computational procedure used to solve conservation equations governing the slip flow in a molecular pump of the Holweck type is developed. The finite volume method is used for discretization and the grid is arranged in the curvilinear, nonstaggered form. The slip boundary condition is imposed on the solid walls. The clearance gap between the rotor and the casing is ignored. It is evident from the calculation that the pressure difference between the two side walls of the channel, termed pressure side and suction side, varies in accordance with the pressure difference between the inlet and the outlet of the pump. Thus, the side-wall pressure difference can play the role of an indicator of pumping effectiveness. Tests on a variety of configurations show that to achieve the best performance both the spiral angle and the channel height need to be optimized. Besides, it is better to have fewer flow channels and to place these channels on the rotor instead of on the casing.